An Arabidopsis gene, AtCEP1 (C-terminal encoded peptide), encoding a 14 or 15 amino acid secreted ligand has been previously described and reported to influence primary root growth (Ohyama K, Ogawa M, and Matsubayashi Y (2008), “Identification of a biologically active, small, secreted peptide in Arabidopsis by in silica gene screening, followed by LC-MS-based structure analysis”, The Plant Journal 55(1):152-160). AtCEP1 corresponds to 1 CEP1 according to the nomenclature used herein.
In International patent publication no. WO 2013/104026, the entire disclosure of which is incorporated herein by cross-reference, we previously reported studies wherein a number of CEP peptides were identified across a broad range of plant families (angiosperms and gymnosperms), and some of these characterised. Phylogenetic and genetic tools were used to examine the distribution and function of this multigene family, and analyses indicated that this family of genes is unique to higher plants and, surprisingly, occur in root knot nematode (RKN) genomes. Generally, these genes encode secreted peptides that contain 14-15 amino acid long conserved domains. Over-expression studies were used to demonstrate that CEP peptides affect multiple aspects of root architecture and development including lateral root, nodule and root hair development, as well as shoot to root ratio.